Certain embodiments of the present invention relate to an ultrasound machine for displaying an image of moving structure. More particularly, certain embodiments relate to providing real-time visualization of movement parameter gradients in such an image.
Echocardiography is a branch of the ultrasound field that is currently a mixture of subjective image assessment and extraction of key quantitative parameters. Evaluation of cardiac wall function has been hampered by a lack of well-established parameters that may be used to increase the accuracy and objectivity in the assessment of, for example, coronary artery diseases. Stress echo is such an example. It has been shown that the subjective part of wall motion scoring in stress echo is highly dependent on user training and experience. It has also been shown that inter-observer variability between echo-centers is unacceptably high due to the subjective nature of the wall motion assessment.
Much technical and clinical research has focused on the problem and has aimed at defining and validating quantitative parameters. Encouraging clinical validation studies have been reported, which indicate a set of new potential parameters that may be used to increase objectivity and accuracy in the diagnosis of, for instance, coronary artery diseases. Many of the new parameters have been difficult or impossible to assess directly by visual inspection of the ultrasound images generated in real-time. Often, processing-intensive mathematical calculation of the parameter gradient is required. In other situations, quantification has required a post-processing step with tedious, manual analysis to extract the necessary parameters.
Much of the prior art describes techniques for color mapping estimated imaging parameters such as tissue velocity and strain rate. A fixed mapping of a continuous range of color hues is typically used to indicate positive velocities or strain rates and a second fixed mapping of a continuous range of color hues is used to indicate negative velocities or strain rates.
However, color schemes in prior art are not well suited for visual determination of other parameters such as velocity gradients or motion gradients. Typically, a Nyquist velocity and associated pulse repetition frequency is set in order to avoid aliasing. A problem in parasternal views, for example, is that there may be a large range of actual velocities or actual motion values. But a localized myocardial gradient, for example, may occupy only a small fraction of the overall velocity or motion range. Typical prior art color encoding of, for example, a 2-dimensional sector display may, therefore, not be capable of actually separating the velocities or motion values between, for example, endocardium and epicardium with clearly differentiating colors. Quantitative assessment through visualization of parameters such as velocity and motion gradients from localized areas in 2-D images has been difficult, even in lucky situations, with an optimum spread of measured imaging parameters. It has often been necessary to resort to post-processing techniques and manual extraction of the digital information used in the color encoding for estimation of parameter gradients. In other scenarios, processing-intensive mathematical calculations of the parameter gradient are required.
For example, U.S. Pat. No. 5,615,680 (Sano, issued Apr. 1, 1997) describes real-time calculating of velocity gradients (average slopes) between a plurality of regions using a least squares technique and then displaying brightness levels to indicate gradients between the regions. According to Col. 18, lines 20-23 and FIG. 28, a red tone is allocated to segments whose associated average slopes are lower than a threshold, and a blue tone is allocated to segments whose associated average slopes exceed the threshold.
U.S. Pat. No. 5,820,561 (Olstad, et al., issued Oct. 13, 1998) describes display of velocities in M-mode polygons. A user may view velocity variations to attempt to determine velocity gradients between the polygons (Col. 5, lines 42-54).
None of the foregoing patents, however, describe or suggest user control to set a desired parameter range of values and a desired color legend so that gradients may be readily estimated by a user.
A need exists for a simple, yet robust approach to easily visualize gradients of tissue motion parameters, such as strain rate, in a two-dimensional ultrasound image.
An embodiment of the present invention provides an ultrasound system for generating an image responsive to gradients of motion parameters that are representative of tissue motion.
An apparatus is provided in an ultrasound machine that is arranged to generate an image responsive to moving structure within a region of interest of a subject. The movement of the structure is defined by a movement parameter. A user of the machine may visually estimate gradients of the movement parameter of the structure by displaying color hues corresponding to ranges of values of the movement parameter. In such an environment the apparatus for displaying the color hues comprises a user interface to enable the user to define a plurality of ranges of values of the movement parameter and to assign selected color hues to the ranges. A front-end is arranged to generate transmitted signals into the structure and then to generate received signals in response to ultrasound waves backscattered from the structure. A processor is responsive to the received signals to generate a set of parameter signals representing values of the movement parameter within the structure and within the plurality of ranges of the movement parameter during a time period. A display is responsive to the set of parameter signals to display an image of the structure within the region of interest with color hues corresponding to the plurality of ranges of values of the movement parameter. A color legend comprising the color hues and indicating a correspondence between the ranges of values of the movement parameter and the color hues is also displayed.
A method is also provided in an ultrasound machine that is arranged to generate an image responsive to moving structure within a region of interest of a subject. The movement of the structure is defined by a movement parameter. Gradients of the movement parameter of the structure may be visually estimated by displaying color hues corresponding to ranges of values of the movement parameter. In such an environment, the method for displaying the color hues comprises enabling a user to define a plurality of ranges of values of the movement parameter and assigning selected color hues to the ranges. Signals are transmitted into the structure and then received in response to ultrasound waves backscattered from the structure within the region of interest over a time period. A set of parameter signals representing values of the movement parameter within the structure and within the plurality of ranges of the movement parameter is generated in response to the received signals. The image of the structure is displayed within the region of interest represented by the color hues corresponding to the plurality of ranges of values of the movement parameter. A color legend comprising the color hues and indicating a correspondence between the ranges of values of the movement parameter and the color hues is also displayed.
Certain embodiments of the present invention afford an approach for visualizing parameter gradients of moving structure on a color display in real-time with a degree of convenience and accuracy previously unattainable in the prior art without requiring a real-time mathematical calculation of the parameter gradient.